Acknowledgment
The authors are indebted to Tadeusz Kowalczyk, Dept. of Veterinary Science; E. C. Zehner, Dept. ofDairy Husbandry; and Sally Jo Krueger and Lydia MCBride, Dept. of Entomology, University of Wisconsin, for their skilled technical assistance. and to Gerhard Schrader, Farbenfabriken Bayer A.-G.? Leverkusen. Germany. for supplying samples of phosphorus-32-labeled Co-ral and a known oxygen analog. The advice and assistance generously provided by Rosmarie \-on Rumker, Dan MacDougall. C. .4. .4nderson, and J. S . Skaptason of the Chemagro Corp.; W. E. Robbins and J. K. Kaplanis of the Entomology Research Branch, U.S.D.A.; and C. S . Schroeder of the Dept. of Biochemistry. L-niversity of M’isconsin are gratefully acknowledged. Literature Cited
(1) Bombinski. T. J., Dubois. K. P.. L-niversity of Chicago. unpublished
results, 195’. (2) Bowman, J. S.: Casida. J. E.. J. AGR. FOODCHEM.5 , 192 (1957). (3) Brundrett. H . M., McGregor. W. S.. Bushland, R . C., Agr. Chemicals 12, 36 (1957). (4) Casida. J. E., Chapman, R. K.. Allen. T . C . ? J . Econ. Entomol. 45, 568 (1952). (5) Casida. J. E.? Gatterdam, P. E.? Knaak, J. B., Lance, R . D.! Xiedermeier, R. P., J. AGR. FOODCHEM.6, 658 (1958). (6) Chemagro Corp.. mimeographed circular announcing availability of Co-ral for experimental use, August 1957. ( 7 ) Comar. C. L., “Radioisotopes in Biology and Agriculture,” p. 130, McGraw-Hill, S e w York, 1955. (8) Elderfield. R . C., Meyer, V. B.. “Heterocyclic Compounds.” Vol. 2, Chap. 1. R. C. Elderfield, ed., Wiley. New York. 1951. (9) Hein, R . E.. McFarland. R . H.: J . A m . Chem. Soc. 74, 1856 (1952). (10) Krueger, H. R.. Casida. J. E.? J . Econ. Entomol. 50, 356 (1957). (11) Lindquist, D . A.: Burns, E. C.. Pant, C. P.: Dahm, P. A . , Zbid.: 51,
204-6 (1958). (12) Plapp, F. W., Casida. J. E.: d n a l . Chem. 30,1622 (1958). (13) Plapp. F. FV.. Casida. J. E.. J. AGR.FOODCHEW6, 662 (1958). (14) Plapp. F. \V.. Casida. J. E.? J . Econ. Entomol.. 51, 800 (1958). (15) Radeleff. R . D.. F\’oodard. G. T.. A g r . Chemicals 12, 36 (1957) (personal communication). (16) Robbins, FV. E.. U. S . Dept. of Agriculture. Beltsville, Xld.: personal communication, 1957. (17) Roth. .4. R.. Eddy. G . \V..J . Econ. Entomol. 48, 201 (1755). (18) Smith. C. L.. Richards, R . , Zbid.. 47, 712 (1954). (19) FYawzonek, S.. “Heterocyclic Compounds.” 1’01. 2, Chap. 6: R. C. Elderfield. ed.: \$ley, New York, 1951. Receired f o r reciew June 23, 7958. Accepted January 5, 7959. &$raced for publication by the director of the T.1’isconsin .4gricultural Experiment Station. This study w a s supported in part by research grants from the Chemagro Corp., C*, S. Atomic en erg,^ Commission (Contract -Vo. A T ( 7 7-71-64 project JVO. 74), and Regional Rest-arch Project ‘VC-33.
A N I M A L METABOLISM OF I N S E C T I C I D E S
Bovine Metabolism of Organophosphorus Insecticides. Metabolism and Residues Associated with Oral Administration of Dimethoate to Rats and Three Lactating Cows
W. C. DAUTERMAN, J. E. CASIDA, J. B. KNAAK, and TADEUSZ KOWALCZYK 1
Departments of Entomology, Dairy Husbandry, and Veterinary Science, University of Wisconsin, Madison, Wis.
Dimethoate is active as a systemic insecticide for cattle. Three lactating cows were treated orally with the radioactive compound and analysis of blood, tissues, excreta, and milk showed Dimethoate to be rapidly metabolized and excreted. Twelve days after treatment, the insecticide was found in trace amounts only in the cow tissues. Hydrolysis of Dimethoate by rats and cows occurred initially at the methyl-phosphate, phosphate-sulfur, sulfur-carbon, and particularly at the carbonyl-nitrogen bonds. Phosphorothioate oxidation occurred with certain of the hydrolysis products and was assumed to occur also with Dimethoate.
D
or Am. Cyanamid 12,880 [O,O-dimethyl s-(~vmethylcarbamoyimethyI)phos p h o r o d ithioate] has shown promise as a chemotherapeutic agent for the control of cattle grubs. Oral administration to calves of 10 to 40 mg. per kg. yields excellent grub control (5). When tested as a n animal systemic against Aedes mosquitoes, it gave excellent control during the first 24 hours, but decreased rapidly thereafter (4). This study concerns the residues and metabolites associated with the proposed use of Dimethoate as a n animal systemic insecticide. IMETHOATE
188
Methods and Results
Synthesis and Characterization of Radioactive Studies Dimethoate Derivatives. Radioactive 0,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate was prepared from phosphorus-32 pentasulfide obtained by neutron irradiation (Atomic Energy Commission, Oak Ridge, Tenn.) or by isotopic exchange with phosphoric-32 acid ( I ) . Radioactive 0,O-dimethyl phosphorodithioic acid was then prepared ( 9 ) and neutralized with potassium hydroxide to yield the potassium salt in aqueous solution. An amount of N-methyl a-
A G R I C U L T U R A L A N D FOOD CHEMISTRY
chloroacetamide equimolar to the potassium 0,O-dimethyl phosphorodithioate was dissolved in water, layered with chloroform, and the two-phase system stirred rapidly and refluxed a t 85’ C. as the potassium 0,O-dimethyl phosphorodithioate solution was added dropwise over a 30-minute period (74). After an additional 15 minutes of refluxing, the chloroform layer was separated. and the aqueous phase extracted three times with an equal volume of chloroform. The product formed in 60% yield had a specific activity of about 5 mc. per gram and it was purified on a silica gel column (Figure 1). O,O,S-
z
?
0
z 4 W
2 4 _I LL W
LITERS
REAGENT
Figure 1. Chromatographic separation on silica gel columns, of Dimethoate and certain possible metabolites
Trimethyl phosphorodithioate, present as an impurity of less than 1.0% was removed by this column purification. The radioactive product was identical in infrared spectrum and rate of hydrolysis in 0.1 molar aqueous sodium carbonate to a known sample of highly purified Dimethoate. Radioactive 0,O-dimethyl S-carboxymethyl phoijphorodithioate-designated as the carboxy derivative of Dimethoate-was prepared in ?Oy0yield according to the same procedure as for Dimethoate except 'that a-chloroacetic acid replaced :\.-methyl a-chloroacetamide ( 7 4 . This radioactive product \vas identical in chromatographic propertirs and infrared spectrum to a known nonradioactive sample supplied by American Cyanamid Co. Radioactive plstassium 0-methyl S(.I--methylcarbamoylmethyl) phosphorodithioate-designated as the des-methyl derivative of Dimethoate--\vas prepared by refluxing 1.0 molar equivalent of radioactive Dimethoate with 1.6 molar equivalents of nonradioactive potassium 0.0-dimethyl phosphorodithioate in acetone for 2 hours (14). The acetone was then evaporated. the residue dissolved in water and extracted first with nhexane and then \vith chloroform. The n-hexane extract contained 0.8 molar equivalent of (3.0,s-trimethyl phosphorodithioate which was identified by comparison of its infrared spectrum with that of the known derivative. Unreacted Dimethoate was present in the chloroform extract based on a n infrared spectrum. The \rater \vas removed under reduced pressure to leave the potassium salt of the radioactive desmethyl derivativr and nonradioactive potassium 0,O-c.imethy1 phosphorodithioate. These salts \\ere insoluble in chloroform but could be readily converted to the fre,? acids by reaction in acetone xvith hydrochloric acid followed by filtration to remove the potassium chloride. it'hen the radioactive desmethyl derivative was chromatographed on a n ion exchange column, it \vas eluted as a single radioactive compound in a position diffcrent from (the other) known phosphorothioic acid esters investigated (Figure 2). Dimethoate and the carboxy deriva-
Figure 2. Ion exchange separation on Dowex 1 of metabolites of Dimethoate Reagents: I, elution gradient p H 2 to p H 1 HCI; II, elution g r a dient p H 1 HCI plus methanol ( 1 to 3) to 1 N HCl plus methanol ( 1 to 3); 111, elution gradient 1 N HCI plus acetone ( 1 to 3 ) to concentrated HCI, water, and acetone ( 1 to 1 to 6); IV, concentrated HCI, water, and acetone (1 t o 1 t o 6 )
rive were individually reacted \\-ith equimolar anhydrous peracetic acid in chloroform for 12 hours a t 28" C. The oxidation products were purified on a silica gel column. The yields from Dimethoate and the carboxy derivative of products chromatographing in a position different from the original phosphorothioates were about 30 and 457,, respectively (Figure 1). When the oxidized carboxy derivative was chromatographed on an ion exchange column, only 0,O-dimethyl phosphoric acid was recovered indicating instability under these conditions. Infrared spectra on the oxidized Dimethoate (DimethoateP=O) and the oxidized carboxy derivative after purification on silica gel were almost identical with the phosphorodithioates with the exception of the loss of an absorption peak a t 15.6 microns and the formation of a strong peak a t 8.0 microns. These spectral changes are consistent with the formation of phosphorothiolate derivatives through oxidation with peracetic acid. The infrared spectra were obtained with the compounds as 10% solutions in chloroform using sodium chloride optics in a Baird Model B double beam infrared spectrophotometer. Dimethoate, Dimethoate- P=O: the carboxy derivative, and the carboxy P=O showed carbonyl absorption peaks at 6.0: 6.0, 5.9, and 5.9 microns? respectively. Dimethoate and its oxygen analog had a n N-H stretching peak a t 3.0 microns, Jvhile the latter three compounds had a broad peak a t 3.4 microns. Partition and Ion Exchange Chromatography. Partition chromatography with silica gel columns (73) served to separate certain Dimethoate impurities and possible metabolites (Figure 1). Dimethoate. the carboxy derivative and O,O,S-trimethyl phosphorodithioate were readily separated with different hexanechloroform mixtures, while the phosphorothiolate analogs bvere all eluted with chloroform. Ion exchange chromatography (70) separated several hydrolysis products of Dimethoate ivhen a n elution gradient V O L . 7,
of hydrochloric acid, methanol, and acetone were employed (Figure 2). Rate o f Excretion Metabolism Of and Nature of ExDimethoate and cretory Products. Derivatives One -hundred and in Rats fifty-gram male and female rats were treated orally at 100 mg. per kg. with radioactive Dimethoate in corn oil solution via a stomach tube. The cumulative per cent excretion was determined separately for the sexes using metabolism cages which allowed separation of the urine and feces ( 3 ) . Four female and 10 male rats were used. The results are shown in Figure 3. The nature and proportions of the hydrolysis products excreted in the urine by the male rats were analyzed using ion exchange chromatography (Table I). The proportion of 0,O-dimethyl phosphoric acid increased with time after administration. However, the remaining identified hydrolysis products did not change appreciably in proportion during the same period of time. Rats were also treated orally bvith the radioactive Dimethoate-P=O, carbosy and des-methyl derivatives. The urine from two surviving male rats treated orally at 50 mg. per kg. with DimethoateP=O was collected a t 12, 24, and 48 hours, The cumulative per c e i t of the administered radioactivity excreted over the indicated times isere 16. 19. and 307,? respectively. Utilizing ion exchange chromatography the metabolites found in the 48-hour urine composite were 0,O-dimethyl phosphoric acid, unknown '4, 0,O-dimethyl phosphorothioic acid! and unknown B a t 34. 52: 9.5, and 4.57,, respectively. Radioactive carboxy derivative was administered orally to three male rats a t 100 mg. per kg., and a sample of the 24-hour urine composite \vas chromatographed. The metabolites found were the carboxy derivative: 0.0-dimethyl phosphorodithioic acid, 0,O-dimethyl phosphorothioic acid, and 0.0-dimethyl phosphoric acid a t 65, 23, 9. and 3 7 ~ . respectively. Radioactive des-methyl derivative was administered to rats a t ~
-
N O . 3, M A R C H 1 9 5 9
189
Table 1.
Nature
Hours offer Administrafion
of Dimethoate Metabolites in the Urine of Male Rats and
a Steer Treated Orally at 100 Mg. per Kg.
Various Hydrolysis Producfs in fhe Urine, % Corboxy (CHzO)*P(S)OH (CHBO)UP(S)OH Des-mefhyl
+
(CHaO)sP(O)OH
Corboxy
6.2 19.6 11.4 12.4 17.6 21.7
32.4 21.1 42.4 ... 35.2 22.0
12 5
...
63.4'1
2.1 4.3 11.9 28.0 44.4 56.3 45.7
74.0
... 81 5,l 61 Ofg ..
4 12 18 24 48
Composite 0168 hrs.
...
MALERATS 20 5
...
25 8 20 4
... 63.9~ ... ...
26 6 32
-
(CH8O)?P(S)SH
Unknowns A i - 6
12.0 5.2 1.2 1.2 1.8 5.5
23.4 18.3 21.4 21 . o 17.2 17.4
5.5 10.0 3.2 1.5 1.6 0.7
2.7
19 2
2 2
2.1 2.1 8.1 10 3 8.3 2.7 3.9
11.6 6 2 15.1 8.0 6.9 7.4 17.4
1.2 2 9 3.9
STEER 1.2 2 3 4.2 6 1 12.3 19.6 30.1
... ... 22.9 11.1
...
18.3
3 1'. Of*
...
9.0 . . .
25 9 25.8 ... 12.5
I .9 3.5 2.6 2.2
Composite*of 0 to 30.1 hrs. 32.6 f 2 . 1 24.8~ 45.8 f 0.67 21 . o c 7.1 i 1.1 12.6 f 4.0 1.9 f 1.7 * Variability from three 5 The resolution of these columns was inadequate to differentiate the carboxy and (CH,O)UP(S)OH fractions. analyses indicated as standard deviation. c Average of two values. 1
1001
Table II. Tissue Residues Expressed as Total Parts per Million Dimethoate Equivalents after Oral Administration of Dimethoate to M a l e Rats at 100 Mg. per Kg. Dimefhoofe Equivolenfs, P.P.M., offer Hours lndicafed
.
DAYS
AFTER
.
ADMINISTRAT
Figure 3. Cumulative per cent excreted by male and female rats treated at 100 rng. per kg. of Dimethoate
10 mg. per kg., and the 12-hour urine sample was chromatographed. Eightyfive per cent of the radioactivity which !vas excreted in the urine chromatographed with nonradioactive des-methyl carrier. The remaining 15% was eluted, with no definite peak, before and after the des-methyl peak. Tissue Residues. Samples of 21 tissues were taken at the time of sacrifice of the Dimethoate-treated rats and the total parts per million of Dimethoate equivalents were determined. A portion of the data from the male rats is presented in Table 11. The highest levels of total radioactivity persisted in the skin, liver, and bone. The dissipation rate of the radioactivity from the kidney was similar to that from the spleen, pancreas, lung thymus, adrenals reproductive tract, submaxillary glands, and lymph nodes. A t 24 hours the stomach wall, caecum wall, large intestine, and small intestine, with their respective contents, were the highest of the tissues in total radioactivity. However, the radioactivity in these tissues diminished to below the level in the liver by 72 hours. At 168 hours after treatment, the total Dimethoate equiv-
190
Tissue
24
72
7 68
336
Liver Heart Kidney Brain Fat Muscle Skin Blood Bone
10.1 2.1 5.6 1.1 2.0 1.6
2.0 0.08 0.61 0.26 0.32 0.25 4.1 0.11 1 .80
1.2 0.12 0.38 0.49 0.30 0.29 1.8 0.14 1.8
0.58 0.22 0.20 0.14 0.11
5.9 2.8 2.8
alents in the tissues from the female rats were 2 to 5 times the level found in the male rats, but this difference was less consistent after 672 hours. Treatment and Metabolism Of Handling of the Dimethoate by Cows. Radioactive Lactating Cows mixed with bran, encapsnlated in gelatin capsules was fed to three lactating cows. One Holstein cow was treated at 40 mg. per kg. while two Jersey cows were treated at 10 and 9 mg. per kg. The three cows were catheterized and held in metabolism stalls to allow for the total separation and collection of urine and feces. Samples of jugular blood? subcutaneous fat, urine, feces, and milk were periodically taken for analysis. The Holstein cow and one Jersey cow were sacrificed 144 hours after administration of Dimethoate; the remaining cow was sacrificed after 288 hours. Rate of Excretion and Nature of Excretory Products. The percentages of the 9, 10, and 40 mg. per kg. doses excreted during the first 24 hours were 73.0, 72.0, and 55.3, respectively in the urine, and 2.4, 3.2>and 2.4, respectively, in the feces. Urine samples from a steer treated
AGRICULTURAL AND FOOD CHEMISTRY
0.08 2.1
...
...
672
0.53 0.07 0.03 0.16 -.-.-.
40 m g / k g cow 'L.
HOURS
AFTER
ADMINISTRATION
Figure 4. Blood cholinesterase (corpuscle) depression curves for cows fed encapsulated Dimethoate
The carboxy derivative of Dimethoate was the predominant hydrolysis product shortly after treatment of the steer. As the pxoportion of carboxy derivative and dimethyl phosphorothioic acid decreased. there was an almost corresponding increase in the proportion of dimethyl phosphoric acid. The other hydrolysis products were excreted in more uniform proportions throughout the 30.1-hour ptriod. Fractionation of the urine from :he three lactating cows a t various times after treatment showed the same general relationship in the proportion of the various hydrolysis products. A composite sample of the total feces excreted by the co\v treated with 9 mg. per kg. of Dimetihoate and held 288 hours was extracted with water and chloroform by a similar m s h o d to that described later for the tissue extractions. The chloroform-soluble radioactivity was chromatographed with nonradioactive Dimethoate carrier on a silica column. Of the administered dose. 3.770 of the total radioactivity appeared in the feces, with 0.01 5% as chloroform-soluble radioactive compound(s) and only 0.0015% as radioactive compound chromatographing in a similar manner to Dime thoate. Dimethoate Equivalents in Blood and Cholinesterase Depression. T h e cholinesterase activity of the jugular blood was determined manometrically ( 2 ) . .4 sharp depression in blood cholinesterase activit). occurred for the cow treated with 40 mg. per kg. within 4 hours after treatment (Figure 4). Symptoms of phosphate poisoning occurred a t 24 hours a t which time the treated animal went off feed and developed diarrhea. The cow appeared to have fully recovered 96 hours after administration of the compound. h-o symptoms of phosphate poisoning were observed in the cokvs treated with 9.0 and 10.0 mg. per kg. nor were any gross pathological abnormalities observed in any of the organs and tissues recorded in Table IV when the three COWS were sacrificed. The total parts per million of Dimethoate equivalents reached a maximum in the blood 3 hours after treatment
HOURS (LOG. SCALE)
HOURS
Figure 5. Average parts per million of total Dimethoate equivalents in the blood and subcutaneous fat from the 9.0- and 10-mg.-per-kg. cows
(Figure 5). The blood was fractionated by diluting 3 ml. of blood to 25 ml. with water and extracting three times with a n equal volume of rhloroform. The chloroform-soluble radioactivity in the blood reached a maximum of 1.5 p.p.m. a t 2 hours for the 9.0- and 10.0-mg.per-kg. cows; after 48 hours, less than 0.03 p.p.m. of chloroform-soluble radioactivity was found. Dimethoate Equivalents in Milk. Dimethoate plus its metabolites were secreted in the 0- to 8-hour milk to the extent of 1.5 p.p.m. (Figure 6). For the fractionation of the milk. 100-ml. samples were mixed in a Waring Blendor with 200 ml. of chloroform. After centrifugation. the chloroform and protein layers were filtered through Celite on a Buchner funnel. The mixed Celite and protein layer \vere then mixed with 200 ml. of acetone in a b'aring Blendor. chilled and filtered. The acetone and chloroform extracts were combined and evaporated. The milk fat was then dissolved in hexane and extracted three times with an equal volume of acetonitrile to recover the Dimethoate in the acetonitrile fraction. T h e acetonitrile was evaporated, the radioactivity determined and further fractionated by chromatography on silica gel column with nonradioactive carrier Dimethoate. The per cent recovery of Dimethoate in milk was determined by adding 4 p.p.m. of radioactive Dimethoate initially to a control milk sample. Immediately after the addition of Dimethoate. the milk sample was fractionated as described previousl?.. Recovery of Dimethoate was only 65%. With the cow' treated a t 9.0 mg. per kg.. the chloroform-soluble Dimethoate equivalents in the milk were less than 0.02 p.p.m. after 48 hours (Figure 6). By extracting a composite sample representing the total milk secreted over a 288hour period, only 20% of the chloroformsoluble radioactivity chromatographed coincidently \vith nonradioactive carrier Dimethoate. This corresponded to 0.0043 p.p.m. of actual Dimethoate secreted in the milk from the composite
AFTER
ADMINISTRATION
Figure 6. Secretion of Dimethoate and derivatives in milk of a cow after oral administration of 9.0 mg. per kg.
or 0.00687c of the administered dose of Dimethoate. The COM treated with 40 mg. per kg. secreted 9.5 p,p.m. of total Dimethoate equivalents or 4 0 p.p.m. chloroform-soluble equivalents in the 0- to 8-hour milk sample. Forty-eight hours later, only 0.04 p.p.m. of chloroform-soluble Dimethoate equivalents were secreted in the milk. Partitioning of Dimethoate into and out of Fat in Vivo. Biopsies of subcutaneous back fat \.\.eretaken from the cows treated a t 9.0 and 10.0 mg. per kg. at various times after the administration of the radioactive Dimethoate. The total p , p , m , of Dimethoate equivalents in the fat compared \vith Dimethoate equivalents in the blood are shown in Figure 5. The total Dimethoate equivalents reached a maximum in the fat and the blood 3 hours after treatment. The fat was fractionated by mincing the tissue with 2 5 ml. of water and 100 ml. of chloroform in a M'aring Blendor. The remainder of the extraction procedure was identical to that utilized for the milk fractionation. The chloroformsoluble radioactivity reached a maximum in the fat a t 3 hours with 0.95 p.p.m. and dropped belolv 0.1 p.p.m. at the 8hour period. Tissue Residues. Samples of 34 tissues were taken on sacrifice of the cows and the total parts per million of Dimethoate equivalents were determined (Table 111 and I\'). Liver, heart. kidney, brain, subcutaneous fat, and loin muscle samples were fraaionated. Fiftygram tissue samples were minced with 100 ml. of water and 200 ml. of chloiolorm in a Waring Blendor. After centrifugation. the chloroform and protein layers were filtered through Celite on a Buchner funnel. The mixed Celite and protein layer was then mixed with 200 nil. of acetone in a Waring Blendor. chilled, and filtered. The remainder of the fractionation procedure was identical to the milk extraction. Table I11 presents the parts per million of total Dimethoate equivalents and chloroform soluble equivalents for the tissues fractionated. The chloroform-soluble radioactivity was chromatographed with nonradioactive carrier Dimethoate to deter-
VOL. 7 , NO. 3, M A R C H 1 9 5 9
191
Table 111.
% Recovery" zk Std. Dev. Used for Correction
Tissue
Nature of Tissue Residues in Dimethoate-Treated Cows
-
9.0 M g . / K g . - 2 8 8
Total
CHCIg solubles
Dimethoate Equivalent, P.P.M., in Fraction Indicated Hours 10.0 M g . / K g . - I44 Hours Dimethoate
Total
CHC13 solubles
Dimethoate
40.0 M g . / K g . - I44 Hours Total
CHC13 solubles
Liver 69.8 z k 2 . 9 2.1 0.23 0.026 4 4 0.45 0.075 5.0 0.62 Heart 59.6 i6 . 2 0.17 0.052 0.003 0.24 0.084 0.006 0.93 0.35 Kidney 63.5 i4 . 6 0.26 0.14 0.013 0.55 0.19 0.10 1.7 0.25 Brain 51.6 i6 . 5 0.13 0.083 0.004 0.15 0,097 0.009 1.8 0.91 Fat subcutaneous 7 4 . 4 i 5 . 0 0.007 0,0052
